BackgroundThe group II metabotropic glutamate receptor 3 (mGlu3) is an emerging therapeutic target for schizophrenia, as research has demonstrated a link between mutations in the human gene encoding for mGlu3, GRM3, and clinical diagnosis of schizophrenia. Schizophrenia is known to be accompanied by debilitating cognitive impairments that negatively impact the overall quality of life of the patient. While current pharmacological therapeutics mainly target the positive symptoms, cognitive symptoms are often not effectively treated. Our recent discovery that mGlu3 and mGlu5 can act as signaling partners to modulate synaptic plasticity in the prefrontal cortex led us to hypothesize that mGlu3 may subserve similar functions to those of mGlu5 during hippocampal synaptic plasticity and hippocampal-dependent behaviors.MethodsWe directly tested this hypothesis using acute slice electrophysiology to investigate basal synaptic transmission as well as long-term plasticity in hippocampal slices. To test cognition, the associative fear learning behavioral assay, termed trace-fear conditioning, was used. C57bl/6 mice or CaMKII-cre;mGlu5-/- mice were used in all studies.ResultsWe report that mGlu2/3 activation enhances hippocampal theta-burst (TBS)-induced LTP but was without effect on group I mGlu agonist-induced LTD The group II mGlu agonist enhancement of TBS-LTP was blocked by antagonists of mGlu3 or mGlu5.We next tested downstream mechanisms of group II mGlu induced LTP by chemically activating LTP with the group II agonist LY379268 in combination with selective antagonists. We verified the LTP was induced by mGlu3 activation but not mGlu2 using selective negative allosteric modulators of each subtype. Furthermore, mGlu5 negative allosteric modulation with MTEP blocked mGlu3-LTP, and conversely the mGlu5 positive allosteric modulator, VU0092273, enhanced mGlu3-LTP. The cannabinoid receptor type 1 antagonist AM251 was also capable of blocking mGlu3-LTP, suggesting cannabinoid signaling mechanistically drives this LTP.Having confirmed a role for mGlu5 in the mGlu3-LTP, we next verified that postsynaptic mGlu5 located on pyramidal neurons was necessary for mGlu3-LTP by utilizing CaMKII-cre;mGlu5-/- mice. It was found that hippocampal slices from these mice showed no enhancement of LTP when LY379268 was bath applied alone or in combination with TBS-stimulation.Behaviorally, we discovered that selective activation of mGlu3 by systemically injecting the group II mGlu agonist in combination with a selective mGlu2 negative allosteric modulator, VU6001966, causes an enhancement in the acquisition of trace-fear conditioning learning. This was also confirmed to be dependent on mGlu5 as both systemic pharmacological inhibition or genetic deletion of mGlu5 abolished this learning enhancement. Further testing of the ability of mGlu3 activation to augment other cognitive tasks is currently underway.DiscussionThese results taken together demonstrate mGlu3 enhances hippocampal LTP and hippocampal-dependent learning through mechanis...

We demonstrate a novel role of phospholipase D in M1-dependent rodent cortical plasticity and M1 PAMs that do not couple to phospholipase D have functionally distinct effects on cortical plasticity than non-biased M1 PAMs. AbstractHighly selective positive allosteric modulators (PAMs) of the M1 subtype of muscarinic acetylcholine receptor have emerged as an exciting new approach for the potential improvement of cognitive function in patients suffering from Alzheimer's disease and schizophrenia. M1 PAM discovery programs have produced a structurally diverse range of M1 PAMs with distinct pharmacological properties, including different levels of agonist activity and differences in signal bias. This includes the recent discovery of novel biased M1 PAMs that can potentiate coupling of M1 to activation of phospholipase C but not phospholipase D (PLD). However, little is known about the role of PLD in M1 signaling in native systems and it is not clear whether biased M1 PAMs will display differences in modulating M1-mediated responses in native tissue. We now report a series of studies using novel PLD inhibitors and PLD knockout mice to show that PLD is necessary for the induction of M1-dependent long-term depression (LTD) in the prefrontal cortex (PFC).Importantly, biased M1 PAMs that do not couple to PLD not only fail to potentiate orthosteric agonist-induced LTD but also block M1-dependent LTD in the PFC. In contrast, biased and nonbiased M1 PAMs act similarly in potentiating M1-dependent electrophysiological responses that are PLD-independent. These findings demonstrate that PLD plays a critical role in the ability of M1 PAMs to modulate certain CNS functions and that biased M1 PAMs function differently in brain regions implicated in cognition.

43Alcohol use disorder (AUD) affects all sexes, however women who develop AUD may be 44 particularly susceptible to cravings and other components of the disease. While many brain 45 regions are involved in AUD etiology, proper function of the prefrontal cortex (PFC) is 46 particularly important for top-down craving management and the moderation of drinking 47 behaviors. Essential regulation of PFC output is provided by local inhibitory interneurons, yet the 48 effects of chronic drinking on interneuron physiology remain poorly understood, particularly in 49 female individuals. To address this gap, we generated fluorescent reporter transgenic mice to 50 label the two major classes of interneuron in deep layer prelimbic PFC, based on expression of 51 parvalbumin (PV-IN) or somatostatin (SST-IN). We then interrogated PV-IN and SST-IN 52 membrane and synaptic physiology in a rodent model of binge drinking. Beginning in late 53 adolescence, mice received 3-4 weeks of intermittent access (IA) ethanol. One day after the last 54 drinking session, adaptations to PV-IN and SST-IN intrinsic physiology were observed in male 55 mice but not in female mice. Furthermore, IA ethanol precipitated diametrically opposing 56 changes to PV-IN synaptic physiology based on sex. IA ethanol decreased excitatory synaptic 57 strength onto PV-INs from female mice and potentiated excitatory transmission onto PV-INs 58 male mice. In contrast, decreased synaptic strength onto SST-INs was observed following IA 59 ethanol in all groups of mice. Together, these findings illustrate novel sex differences in 60 drinking-related PFC pathophysiology. Discovering means to restore PV-IN and SST-IN 61 dysfunction following extended drinking provides opportunities for developing new treatments 62 for all AUD patients. 63 64 Key words 65 alcohol, prefrontal cortex, synaptic physiology, parvalbumin, somatostatin 66 67 68 Preclinical studies designed to model alcohol-induced changes to PFC function have 87 largely utilized the chronic intermittent ethanol (CIE) exposure paradigm, an animal model of 88dependence. Using CIE and other chronic treatment models, several labs have described 89 dependence-related changes in PFC physiology to be generally characterized by reduced 90 inhibition and enhanced excitatory synaptic activity (Centanni et al., 2017; Hu et al., 2015; Pava 91 and Woodward, 2014; Pleil et al., 2015;Varodayan et al., 2018). In addition, changes in NMDA 92 receptor function (Hu et al., 2015; Kroener et al., 2012), intrinsic properties (Hu et al., 2015), 93 and PFC network activity (Kroener et al., 2012;Woodward and Pava, 2009), have all been 94 ME Joffe et al.Drinking-induced synaptic adaptations to cortical interneurons 4 shown to occur as a consequence of long-term alcohol exposure and withdrawal. While the 95 literature clearly demonstrates that PFC pathophysiology develops during dependence, deficits 96 in PFC function are also associated with maladaptive changes in voluntary drinking (Haun et al., 97 2018; Klenowski et al., 2016; Radk...